This application is a national stage application of PCT International Application No. PCT/EP2006/006545, filed Jul. 5, 2006, which claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2005 031 511.9, filed Jul. 6, 2005, the entire disclosure of which is herein expressly incorporated by reference.
The invention relates to a control valve for a refrigerant compressor.
A generic control valve and a generic refrigerant compressor are disclosed in German patent document DE 38 22 465 A1. The refrigerant compressor has a plurality of displacement pistons which operate in a drive housing and which are driven in their conveying movement by a swashplate driven via a driveshaft, a belt pulley and the belt drive of an engine of a motor vehicle. The pistons in this case execute an alternating stroke movement oriented in the axial direction of the associated cylinder bores. The conveying capacity of the refrigerant compressor can be set via the drive housing pressure pc which acts in the cavity of the drive housing and on the rear side facing away from the displacement side of the pistons. Thus, starting from a maximum conveying capacity of the compressor, by increasing the drive housing pressure pc, the suction intake movement of the pistons can be reduced to the setting of a minimum conveying capacity or until the conveying capacity is switched off.
To set the drive housing pressure pC predetermining the conveying capacity, the drive housing of the refrigerant compressor is connected to the suction chamber having the suction pressure pS and to the conveying chamber having the conveying pressure pD. In this case, usually, the drive housing pressure pC is set, when the compressor is in conveying operation, via a rigidly throttled, permanently open line to the suction chamber and via a connection, throttlable in a controlled manner by means of a valve, to the conveying chamber.
One object of the invention is to improve further the conveying capacity and the control of a refrigerant compressor.
This and other objects and advantages are achieved by the control valve and the refrigerant compressor according to the invention. A refrigerant compressor of this type or one controlled by such a valve has conveying pistons which operate in a drive housing and which execute alternating stroke movements in associated cylinder bores of the drive housing. The conveying pistons are moved between a final displacement end position concluding and limiting a displacement movement, on the one hand, and a suction intake end position concluding and limiting a suction intake movement. The displacement movement is directed toward a valve plate delimiting the cylinder bore of the drive housing, opposite the displacement side of the conveying pistons. The valve plate has two contradirectionally closing nonreturn valves, via which the cylinder bore is connected, on the one hand, to a suction chamber of the compressor and, on the other hand, to a conveying chamber of the compressor.
The conveying pistons are driven by a swashplate rotating in the drive housing and having an adjustable angle of incidence. The swashplate is in turn driven via an associated axle, a belt pulley seated on the axle and the belt drive of an engine of the motor vehicle. The drive housing of the refrigerant compressor forms, in the range of rotation of the swashplate, a hermetically sealed-off cavity which is connected to the rear side facing away from the displacement side of the conveying pistons, and in which a drive housing pressure pc acts. With the displacement end position of the pistons remaining the same, the suction intake end position of the pistons can be set by varying the angle of incidence of the swashplate, and thereby varying also the conveying capacity of the refrigerant compressor.
The angle of incidence of the swashplate is varied by setting the drive housing pressure pC acting on the rear sides of the pistons. For this purpose, the cavity of the drive housing is connected via two control lines, on the one hand, to a conveying chamber (with a conveying pressure PD) of the refrigerant compressor and, on the other hand, to a suction intake chamber (with a suction pressure PS) of the refrigerant compressor. The latter lines are controllable via a control valve of the refrigerant compressor. In this case, the control valve has a control body which acts on both control lines and which is driven electromagnetically, so that, via an associated control, for example a magnetic force acting counter to a spring force can be set and, via said magnetic force, a control position of the control body can be set.
In the control valve and/or refrigerant compressor, in this case, both the conveying-side and the suction-side control line can be throttled or can be shut off in a controlled manner. As a result, while the compressor is in operation, the suction-side control line can be closed or highly throttled, so that the bypass stream of conventional control valves and refrigerant compressors, which is discharged from the drive housing to the suction chamber on the invariably throttled suction-side control line, is greatly reduced or is avoided in order to improve the refrigerating capacity.
Since an activation of a control state shutting off the suction-side control line (in particular, a control state that throttles the latter in a directed manner) can be controlled only with difficulty by means of a solely electromagnetically driven control body, (especially in the absence of detected state variables of the refrigerant circuit), the present control valve or the refrigerant compressor has a control body which is driven by means of a pressure cell. A pressure cell of this type makes it possible to drive the control body as a function of pressure variables or pressure differences occurring on the refrigerant compressor or on the refrigerant circuit, so that specific operating pressure states of the refrigerant compressor can directly influence the activation of the control body. Since electromagnetic activation of the control body is regulated as a function of the existing measurement points of the associated control (for example, even as a function only of secondary measurement variables, such as an evaporator outflow temperature), the pressure cell makes it possible to improve the control valve by taking into account direct state variables on the refrigerant compressor.
In one embodiment of the control valve, a pressure cell for driving the control body is provided, which monitors the pressure difference of the atmospheric pressure pA of the vehicle surroundings and the suction pressure pS. As a result, as a function of a desired suction pressure, the control body can be activated to open alternately the conveying-side control line (to reduce the conveying capacity in the case of too low a suction pressure) and the suction-side control line (to increase the conveying capacity of the refrigerant compressor in the case of too high a suction pressure). By direct detection of the suction pressure of the refrigerating system and activation of the refrigerant compressor as a function of the suction pressure refrigerating capacity losses and fluctuations (which may occur, for example, in the case of a control dependent on the evaporator temperature) are avoided.
For particularly effective activation of the control body controlling the two control lines, in one embodiment of the control valve and/or of the refrigerant compressor, magnetic action of the magnet coil controlling the control body is converted directly on the control body or on an armature fastened to the control body. As a result, the force of the electromagnetic action of the coil can act directly on the control body of the control valve and, in the case of given force/displacement conditions on the control body, can particularly advantageously be taken into account as a control variable component, for example for the throttling control of an associated port. This is advantageous particularly in the case of a combined activation of the control body with the aid of various force-applying elements, such as, for example, springs or pressure cells. In this case, via the activation of the electromagnetic coil, action can be taken on the force equilibrium on the control body between resilient elements, a pressure transducer or pressure cell and magnetic action. A different operating point of the control valve (that is, a variable desired suction pressure), can thereby be set, so that, once again, a variable basic refrigerating capacity of the compressor can be controlled.
In one embodiment of the control valve or of the refrigerant compressor according to the invention, in the case of an undisturbed operation and state of the associated refrigerating system, when the operation of the refrigerating system is switched off, the control body can assume a position of rest in which the suction-side control line is shut off. This may be achieved by means of a corresponding coordination of the involved spring or drive and switch elements, the control valve and the associated control preferably being dead in this state. By shutting off the suction-side control line of the control valve, settling of refrigerant condensate in the drive housing of the refrigerant compressor is reduced or avoided while the refrigerating system is at a standstill. Thus, when the refrigerant compressor is started again after a lengthy standstill of the refrigerating system, improved starting refrigerating capacity is achieved.
In another embodiment of the control valve, when the suction pressure falls below an associated minimum operating value, the pressure cell brings the control body into a position that releases the conveying-side control line. As a result, for example in the case of leaks of the refrigerant circuit, no damage to the refrigerant compressor is caused by a readjustment of the refrigerating capacity control if the swashplate is set at too high an angle of incidence. Instead, by releasing the conveying-side control line, the swashplate is brought into a neutral position and damage is thereby avoided.
In still another embodiment of the control valve and/or of the compressor according to the invention, the control body, in a control position, can shut off both control lines simultaneously. Thus, in addition to a control operating state releasing the conveying-side control line (and therefore lowering the conveying capacity), and also in addition to a control operation releasing the suction-side control line (and thus increasing the conveying capacity) of the refrigerant compressor, a holding operating state can also be activated. In the latter state, both the suction-side and the conveying-side control line are shut off, and therefore the set conveying capacity can be held without further control actions and without a refrigerant bypass stream, lowering the conveying capacity, via the control lines. Starting from the control state with control lines closed on both sides, for example, a holding operating state can also be activated, in which, with the conveying-side control line closed, a highly throttled suction-side control line is opened, which then does not discharge a bypass stream of the controlled conveying-side control line, but, instead, merely compensates the compression leakages occurring at the pistons.
In order to ensure particularly simple activation and functionally reliable operation of the control valve and/or of the refrigerant compressor, in one embodiment of the control valve or of the compressor the control body can be movable through an intermediate position between two end positions. In a first end position the conveying-side control line is shut off, while in the intermediate position both control lines are shut off, and in a second end position the suction-side control line is shut off. It is thus possible to provide a basic operating position in which both control lines are shut off both on the conveying side and on the suction side (or, with the conveying-side control line shut off, the suction-side control line is highly throttled), and from which the two oppositely effective control actions, (that is, for increasing and lowering the conveying capacity of the refrigerant compressor, respectively) can be activated, from the basic operating position of the control body, in movements contradirectional to one another. This makes it unnecessary, for example, to run over a contradirectional control state in order to activate a desired control state from the basic operating position.